linux-kernel - Re: Suboptimal inline heuristics due to non-code sections

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Date:   Tue, 01 May 2018 15:37:06 +0000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     namit@...are.com, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Suboptimal inline heuristics due to non-code sections

On Tue, May 1, 2018 at 6:40 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> But if I remove the section completely by removing the
> pushsection/popsection, then copy_overflow() gets inlined.

> So GCC's inlining decisions are somehow influenced by the existence of
> some random empty section.  This definitely seems like a GCC bug to me.

I think gcc uses the size of the string to approximate the size of an
inline asm.

So I don't think it's the "empty section" that makes gcc do this, I think
it's literally "our inline asms _look_ big".

                Linus "does this section directive make me look fat?"
Torvalds